1. Field of the Invention
The present invention relates to a gate commutated turn-off semiconductor device comprising a gate commutated turn-off (GCT) semiconductor switching element capable of commutating most of a main current flowing between an anode and a cathode at a turn-on into a gate side at a turn-off.
2. Description of the Background Art
In a prior-art GTO (Gate Turn-Off) thyristor, to give a signal to a gate electrode, a method of gate connection from one direction (see, for example, a technique disclosed in Japanese Patent Application Laid Open Gazette No. 56-125863 and the like) has been widely adopted. In such a structure, however, it is difficult to immediately stop a main current flowing between an anode and a cathode at a turn-off because of large inductance in a gate of an element.
For this reason, a GCT thyristor which allows reduction of gate inductance in an element has been developed. The GCT thyristor adopts a connection structure comprising a ring-shaped gate connection structure, a ring-shaped gate connection terminal formed on a gate drive substrate and a gate driver for controlling a current flowing in the gate (see, for example, techniques disclosed in Japanese Patent Application Laid Open Gazette Nos. 10-294406 and 8-330572 and the like), instead of the method of drawing a gate current from one direction. This makes it possible to reduce the inductance of a loop including the GCT thyristor, the gate drive substrate and the gate driver (referred to as inductance on the gate side) to about a hundredth of that of the GTO thyristor.
In the GCT thyristor, with the inductance value on the gate side remarkably reduced to be lower than that of the GTO thyristor, a gate reverse current rise rate (diGQ/dt) at a turn-off is raised up to a value about hundredth times as high as that of the GTO thyristor and almost all the main current can be thereby commutated into the gate side in a short time at the turn-off. In other words, it is possible to cut the time required to turn off and make the value of a turn-off gain almost one. Thus, the turn-off characteristics can be improved.
Further, with this, it is possible to suppress a breakdown due to local heat generation inside a semiconductor substrate and as a result, it also becomes possible to control a large current.
FIG. 11 is a plan view showing an exemplary constitution of a gate commutated turn-off semiconductor device including a GCT thyristor in the prior art. This gate commutated turn-off semiconductor device comprises a gate drive substrate 7, a GCT thyristor 100 fixed to the gate drive substrate 7 and a gate driver 200 connected to the gate drive substrate 7. Further, a case 13 is attached to the gate drive substrate 7 so as to cover a lower surface thereof. The case 13 also serves as a reinforcing member to prevent a bend of the gate drive substrate 7 due to a load of the gate driver 200.
FIG. 12 is a cross section taken in the section line Cxe2x80x94C of FIG. 11, and FIG. 13 is a cross section showing an enlarged part of FIG. 12. The GCT thyristor 100 comprises a disk-shaped semiconductor substrate (wafer) 24 having a pnpn structure and a gate region on its outer peripheral side, a cathode strain buffer plate 25 connected to a cathode region of the semiconductor substrate 24 and an anode strain buffer plate 26 connected to an anode region of the semiconductor substrate 24, on its center portion. A cathode post electrode 2 is connected to the cathode strain buffer plate 25 and an anode post electrode 3 is connected to the anode strain buffer plate 26. Further, a conductive cathode spacer 4 is connected to the cathode post electrode 2 and a cathode fin electrode 5 is connected to the cathode spacer 4. An anode fin electrode 6 is connected to the anode post electrode 3. The semiconductor substrate 24, the cathode strain buffer plate 25, the anode strain buffer plate 26, the cathode post electrode 2, the anode post electrode 3 and the cathode spacer 4 are sandwiched and pressed by the cathode fin electrode 5 and the anode fin electrode 6.
The GCT thyristor 100 comprises a ring-shaped cathode flange 20 held by the cathode post electrode 2 penetrating therethrough and a ring-shaped anode flange 23 held by the anode post electrode 3 penetrating therethrough. An insulating tube 21 made of ceramics (e.g., alumina) is provided between the cathode flange 20 and the anode flange 23. In FIG. 12, the semiconductor substrate 24, the cathode strain buffer plate 25, the anode strain buffer plate 26, the cathode post electrode 2 and the anode post electrode 3 penetrate as a unit through the insulating tube 21.
As shown in FIG. 13, a gate electrode 7b is formed on an upper surface of the gate drive substrate 7 to serve as a passage of a current between the gate driver 200 and a gate of the GCT thyristor 100. On the other hand, a cathode electrode 7a is formed on a lower surface of the gate drive substrate 7 to serve as a passage of a current between the gate driver 200 and a cathode of the GCT thyristor 100. Providing the cathode electrode 7a and the gate electrode 7b forms a loop between the gate and cathode of the GCT thyristor 100 and the gate driver 200. With a gate current flowing into this loop at a commutation, the main current flowing between the cathode and anode of the GCT thyristor 100 is immediately stopped.
In the semiconductor substrate 24 of FIG. 12, the gate region is formed on a side of the cathode region and a ring-shaped gate electrode 29 is so formed as to be connected to the gate region. The gate electrode 29 is connected to an inner peripheral side of a ring-shaped gate flange 11, and the gate flange 11, being sandwiched by the insulating tube 21, protrudes from a side surface of the insulating tube 21 and extends towards the outside of the insulating tube 21. A portion of the gate flange 11 extendedly existing outside the insulating tube 21 is threaded into a conductive gate spacer 10 with a screw 12. Further, the gate flange 11 is provided with a bend portion 11a to absorb oscillation and stress caused by a switching operation.
The gate spacer 10 is connected to the gate electrode 7b on the upper surface of the gate drive substrate 7 and threaded into the gate drive substrate 7 with a screw 9. The cathode spacer 4 is connected to the cathode electrode 7a on the lower surface of the gate drive substrate 7 and threaded into the gate drive substrate 7 with the screw 9.
Further, to prevent a short circuit between a pair of the cathode spacer 4 and the cathode electrode 7a and a pair of the gate spacer 10 and the gate electrode 7b due to presence of the screw 9, a screw hole for the screw 9 is provided with an insulating bush 8.
In the above-described gate commutated turn-off semiconductor device, the cathode spacer 4 has a function of holding a load of the gate driver 200 by fixing the gate drive substrate 7 and the case 13 to the GCT thyristor 100. If only this function is needed, a case having a structure in which the case 13 and the cathode spacer 4 are formed as a unit may be used. The cathode spacer 4, however, also has a function of achieving an excellent conductivity with both the cathode post electrode 2 and the cathode fin electrode 5 and a function of achieving an excellent conductivity with the cathode electrode 7a on the lower surface of the gate drive substrate 7. To achieve such an excellent conductivity, it is necessary that the cathode spacer 4 should come into contact with respective surfaces of the cathode post electrode 2, the cathode fin electrode 5 and the gate drive substrate 7 while keeping a highly precise flatness on its surface. For this reason, a conductive disk-like member having a thickness of 5 to 10 mm other than the case 13 is processed to be used as the cathode spacer 4.
Further, as the gate spacer 10, like the cathode spacer 4, a conductive ring-shaped member having a thickness of 5 to 10 mm which is so processed as to have a highly precise flatness on its surface is used in order to achieve an excellent conductivity with the gate flange 11 and the gate electrode 7b on the upper surface of the gate drive substrate 7.
Providing the cathode spacer 4 and the gate spacer 10, however, causes an increase in number of required parts and requiring the highly precise flatness on their surfaces is an obstacle to cost reduction. Further, this causes an increase in weight of the gate commutated turn-off semiconductor device.
Furthermore, in the above-described gate commutated turn-off semiconductor device, to avoid complication in shape of the cathode spacer 4 and the gate spacer 10, the gate spacer 10 is provided on the upper surface of the gate drive substrate 7 and the cathode spacer 4 is provided on the lower surface thereof, instead of providing both the spacers 4 and 10 on one surface of the gate drive substrate 7. Accordingly, the gate electrode 7b is formed on the upper surface of the gate drive substrate 7 and the cathode electrode 7a is formed on the lower surface thereof.
Forming electrode patterns on both the upper and lower surfaces of the gate drive substrate 7, however, requires complicated steps such as inversion of the gate drive substrate 7 in the manufacturing process, and thereby becomes an obstacle to reduction in time and cost required for the manufacture.
Further, for easy attachment and detachment of the gate flange 11 and the cathode flange 20 in maintenance, the gate flange 11 is fixed with the screw 12 and the cathode spacer 4 and the gate spacer 10 are fixed with the screw 9.
Attachment of the screws 12 and 9 to the upper and lower surfaces of the gate drive substrate 7 respectively, however, also leads to complication such as inversion of the gate drive substrate 7 in the manufacturing process and difficulty in detachment of the screws in the maintenance, and therefore becomes an obstacle to reduction in time and cost required for the manufacture and maintenance. Further, for the screw 9, providing the insulating bush 8 is needed to ensure insulation between the gate and cathode, and this is also an obstacle to reduction in time and cost required for the manufacture.
The present invention is directed to a gate commutated turn-off semiconductor device. According to a first aspect of the present invention, the gate commutated turn-off semiconductor device comprises: a gate commutated turn-off semiconductor element having an anode, a cathode and a gate, for commutating a main current flowing from the anode to the cathode into a side of the gate at a turn-off; a gate driver for controlling a current flowing in the gate; and a substrate provided with a circuit pattern on its surface, the circuit pattern electrically connecting the gate and the cathode of the gate commutated turn-off semiconductor element to the gate driver to form an electrical loop, and the gate commutated turn-off semiconductor element has a semiconductor substrate having a cathode region, an anode region and a gate region, in which the gate region is formed on an outer peripheral side of one main surface, the cathode region is formed inside the gate region of the one main surface and the anode region is formed on the other main surface opposed to the one main surface; a gate electrode in a ring shape connected electrically to the gate region; a cathode post electrode connected electrically to the cathode region; an anode post electrode connected electrically to the anode region; an insulating tube being electrically insulative, provided so as to surround the anode post electrode and the cathode post electrode and internally containing at least the semiconductor substrate and the gate electrode; a gate flange having an inner peripheral side connected electrically to the gate electrode and an outer peripheral edge portion protruding from a side surface of the insulating tube; and a cathode flange connected electrically to the cathode post electrode, and in the gate commutated turn-off semiconductor device of the first aspect, the cathode flange and the gate flange each include a branch-like protrusion extending towards an outer periphery thereof, the cathode of the gate commutated turn-off semiconductor element is electrically connected to the substrate and the cathode flange is fixed to the substrate with the branch-like protrusion interposed therebetween, and the gate of the gate commutated turn-off semiconductor element is electrically connected to the substrate and the gate flange is fixed to the substrate with the branch-like protrusion interposed therebetween.
According to a second aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the substrate has a first main surface and a second main surface opposed to the first main surface, the circuit pattern includes a first circuit pattern formed on the first main surface, for electrically connecting the cathode to the gate driver, and a second circuit pattern formed on the first main surface, for electrically connecting the gate to the gate driver, the branch-like protrusion included in the cathode flange is connected to the first circuit pattern, and the branch-like protrusion included in the gate flange is connected to the second circuit pattern.
According to a third aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the substrate has a first main surface and a second main surface opposed to the first main surface, the circuit pattern includes a first circuit pattern formed on the first main surface, for electrically connecting the cathode to the gate driver, and a second circuit pattern formed on the second main surface, for electrically connecting the gate to the gate driver, the branch-like protrusion included in the cathode flange is connected to the first circuit pattern, and the branch-like protrusion included in the gate flange is connected to the second circuit pattern.
According to a fourth aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the gate commutated turn-off semiconductor element further comprises a cathode fin electrode connected electrically to the cathode flange, the cathode flange is a member sandwiched between the cathode post electrode and the cathode fin electrode, and the branch-like protrusion and the member are formed as a unit.
According to a fifth aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the cathode flange is a member surrounding the cathode post electrode, and the branch-like protrusion is formed with another member different from the member fixed thereto.
According to a sixth aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the branch-like protrusion of at least one of the cathode flange and the gate flange has a bend portion.
According to a seventh aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the cathode flange and the gate flange each include at least three branch-like protrusions.
According to an eighth aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the substrate has a reinforcing member fixed to the surface thereof.
According to a ninth aspect of the present invention, in the gate commutated turn-off semiconductor device of the eighth aspect, the gate commutated turn-off semiconductor element further comprises a cathode fin electrode connected electrically to the cathode flange, and the reinforcing member comprises an upright portion perpendicular to the substrate and the cathode fin electrode is fixed to the upright portion.
According to a tenth aspect of the present invention, in the gate commutated turn-off semiconductor device of the first aspect, the branch-like protrusion is provided with a screw hole in the vicinity of its tip portion, the substrate is provided with screw pedestals, a screw penetrates through the screw hole of said gate flange and is threaded to one of the screw pedestals to fix the gate flange to the substrate, and a screw penetrates through the screw hole of said cathode flange and is threaded to another of the screw pedestals to fix the cathode flange to the substrate.
In the gate commutated turn-off semiconductor device of the first aspect of the present invention, since the gate flange and the cathode flange are fixed to the substrate by using neither the cathode spacer nor the gate spacer adopted in the prior-art gate commutated turn-off semiconductor device, it is possible to fix the gate commutated turn-off semiconductor device to the substrate while ensuring cost reduction and prevent an increase in weight of the gate commutated turn-off semiconductor device.
In the gate commutated turn-off semiconductor device of the second aspect of the present invention, since both the first and second circuit patterns are formed on the first main surface of the substrate and it is not necessary to form the electrode patterns on both surfaces of the substrate, unlike the prior-art gate commutated turn-off semiconductor device, it is possible to suppress the time and cost required for manufacture. Further, since the branch-like protrusion of the cathode flange and that of the gate flange are fixed on one surface of the substrate, it is not necessary to perform the step of attaching the screws to both surfaces of the substrate and the like and the working efficiency in the manufacturing process and maintenance is improved.
In the gate commutated turn-off semiconductor device of the third aspect of the present invention, the first circuit pattern is formed entirely on the first main surface of the substrate and the second circuit pattern is formed entirely on the second main surface thereof. This can reduce the inductance on the gate side.
In the gate commutated turn-off semiconductor device of the fourth aspect of the present invention, since the branch-like protrusion and the member sandwiched between the cathode post electrode and the cathode fin electrode are formed as a unit, such a structure can be easily obtained by one press.
In the gate commutated turn-off semiconductor device of the fifth aspect of the present invention, since the cathode flange uses the member surrounding the cathode post electrode, instead of the member sandwiched between the cathode post electrode and the cathode fin electrode, it is possible to reduce the electric resistance between the cathode fin electrode and the cathode post electrode and suppress heat generation caused by the switching operation.
In the gate commutated turn-off semiconductor device of the sixth aspect of the present invention, since the branch-like protrusion has the bend portion, it is possible to fit the position of the branch-like protrusion to a position where the substrate is present. Further, it is possible to absorb the oscillation and stress caused by the switching operation in the bend portion.
In the gate commutated turn-off semiconductor device of the seventh aspect of the present invention, since at least three branch-like protrusions are provided, the gate commutated turn-off semiconductor device becomes unlikely to resonate and twist due to the oscillation and stress caused by the switching operation.
In the gate commutated turn-off semiconductor device of the eighth aspect of the present invention, since the substrate has the reinforcing member fixed to its surface, it is possible to suppress the bend of the substrate.
In the gate commutated turn-off semiconductor device of the ninth aspect of the present invention, since the cathode fin electrode is fixed to the upright portion of the reinforcing member, it is possible to further suppress the bend of the substrate.
In the gate commutated turn-off semiconductor device of the tenth aspect of the present invention, the screw pedestal does not need to have a surface of highly precise flatness, unlike the cathode spacer and the gate spacer in the prior-art gate commutated turn-off semiconductor device, and therefore commercial cheap parts can be used for the pedestal.
An object of the present invention is to provide a gate commutated turn-off semiconductor device which eliminates the necessity of a gate spacer and a cathode spacer and ensures reduction in time and cost required for manufacturing the device.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.